This proposed research is a continuation of our ongoing studies (MH 19514) of the physiology of the agitation-depression reaction accompanying maternal separation in infant pigtailed (M. nemestrina) monkeys. The depressive component of this reaction is thought to represent one of the best animal models of grief and loss related depression. Our work to date demonstrates that profound physiological changes accompany the disruption of this attachment bond. Our objectives include the following: (1) Further define the physiology of separation in pigtailed infants with special emphasis on (a) alterations in the regulation of biological rhythms, including heart rate (HR), body temperature (BT), sleep patterns, EMG, and EEG, (b) changes in EEG patterns and their behavioral correlations, (c) a detailed study of cardiac arrhythmias which accompany separation, (2) Evaluate to what extent the individual variability in the response to separation can be predicted by the Biobehavioral Development Profile (BDP) for the pigtailed monkey, (3) Confirm and extend our pilot data suggesting that separation adversely influences immune system function, (4) Evaluate relative sympathetic and parasympathetic contribution to HR regulation, and determine to what extent such individual differences may be related to the physiological response to separation, (5) Examine the role of peripheral (skin) heat loss on BT regulation, (6) Examine the question of possible species specificity by studying normal behavioral and physiological development and the responses to separation in a second species of Macaque monkey (M. radiata), and (7) To optimally study the relationship between the response to separation and CNS amine systems, we will develop the technology necessary to monitor in vivo CNS amine neutrotransmitter metabolism in unrestrained monkeys by means of implantable electrochemical biotelemetry. All animals will be studied completely unrestrained using an improved version of the totally implantable hybrid multichannel biotelemetry systems of our own design. Behavioral and physiological data will be collected and processed in real time using an online multi-processor computer system.